The invention relates to the operation of a single frequency network or network cluster in which multiple base stations, each providing one ore more radio cells, operate in a coordinated manner such that no handover is required when a user equipment traverses multiple cells.
In EP 15154705.6, a method for operating a Single Frequency Network (SFN) based on knowledge of positions and/or trajectories of mobile terminals is described. In brief, a Resource Control Unit (RCU) function is defined that may either be centrally located or allotted in various entities throughout the communication system. In one alternative, a resource pool with local scheduling, it was proposed to assign a first interference mitigation function (for mitigation of inter-SFN-Cluster interference) to a central RCU entity and a second interference mitigation function (for mitigation of intra-SFN-Cluster interference) to a local (or cluster specific) RCU entity. Furthermore it was described that the local RCU may comprise or control the scheduling functionality of the MAC layer of the air interface technology of the wireless communication system. In this concept the local RCU should “tell” all involved transmission points (eNBs or RRHs) in its respective SFN-Cluster when to send what portion of the data in a synchronous manner.
US 2009/0264125 A1 describes a communications system incorporating handheld units for providing femtocell operations. The handheld unit provides a plurality of radio interfaces to user equipment. The femtocell operates in a similar fashion as a regular cellular base station. Where more than one handheld units operate within a given area, femtocell access point functions may be redistributed between the handheld units.
According to 3GPP TS 36.321 the main services and functions of the MAC (Medium Access Control) protocol layer for LTE include:                a) Mapping between logical channels and transport channels;        b) Multiplexing/de-multiplexing of MAC SDUs belonging to one or different logical channels into/from transport blocks (TB) delivered to/from the physical layer on transport channels;        c) Scheduling information reporting;        d) Priority handling between logical channels of one UE;        e) Priority handling between UEs by means of dynamic scheduling;        f) Transport format selection;        g) Padding and other functions.        
The scheduling aspects c) and e) of the MAC functionality are of particular importance for this invention, as these are vital for the efficient mitigation of intra-SFN-Cluster interference.
The general architecture of a cellular communication network according to the state of the art is depicted in FIGS. 1, 2, 3A and 3B. FIG. 1 shows an example network architecture of an LTE communication system 10 where transmission points 20 are sub-divided into clusters, with two clusters being shown, cluster M 22 and cluster N 24. Each cluster is controlled by a respective resource control unit, RCUM 26 and RCUN 28. The RCUs are in turn controlled by a cluster management unit 30. FIG. 1 shows an infrastructure interface 32 (in case of LTE, this is the S1 interface) between the cluster management unit 30 and a mobile management entity, MME, 34, part of the core network.
In FIG. 2, the actual transmission point 20 (antennas or antenna arrays) on the network side is located at a base station 40. FIG. 2 shows the infrastructure interface 32 and an air interface 36 (in case of LTE, this is the Uu reference point). A protocol stack 38 for the air interface for each of a base station 40 and a mobile terminal 42 is also shown. Termination points of the various LTE protocol layers reside in the base station (“eNB”) and the mobile terminal (“UE”).
FIG. 3A shows an example network architecture of an LTE communication system with a Remote Radio Head (RRH) 44 serving as a transmission point. This RRH 44 is connected to a base station 46 (eNB) for example by means of directed wireless technology or fibre optics, while FIG. 3B shows an example network architecture of an LTE communication system with a Remote Radio Head (RRH) 48 connected to a pool 50 of virtual base stations (eNBs). In FIGS. 3A and 3B the actual transmission points (antennas or antenna arrays) on the network side are represented by Remote Radio Heads (RRHs) that are connected to the base station (or to a pool of base station computation resources) by means of an interface INTERFACE 1 which may be a wireless, wired, or optical interface. For instance, CPRI (common public radio interface) protocols may be used on INTERFACE 1. RRHs have become one of the most important subsystems of current new distributed base stations. The Remote Radio Head contains the base station's RF circuitry plus analogue-to-digital/digital-to-analogue converters, up/down converters and antennas. RRHs also have operation and management processing capabilities and a standardized interface to connect to the “rest” of the base station. RRHs make MIMO operation much easier compared to base stations that include RF circuitry, A/D converters etc. and that are connected to antennas via an analogue interface. RRHs also increase a base station's efficiency and facilitate easier physical location for gap coverage problems.
The protocol stacks for the air interface are also shown in FIGS. 3A and 3B as protocol stacks 60, 62 and 64. Termination points of the various LTE protocol layers except for the LTE physical layer, PHY, reside in both the base station (“eNB”) and the mobile terminal (“UE”). In contrast to FIG. 2, at least parts of the LTE PHY layer terminates in the RRH. When looking from the UE's perspective, the counterpart of the PHY layer is located in the RRH, whereas the counterpart of layers above PHY is located in the eNB. INTERFACE 1 is for the exchange of base band signals, while an interface INTERFACE 2 is the actual air interface (antenna to antenna) that uses the resource grid (as described in the previous invention), modulation, and coding schemes of the LTE physical layer.
While in FIG. 3A the RRH is connected to a real physical base station, in FIG. 3B the RRH is connected to a pool of base station computation resources (also known as a “Cloud RAN”).
It is to be noted that a meaningful positioning of the “local RCU” entity in the wireless communication system depends very much on the actual deployment scenario. More specifically, it depends on the topological network structure and the answer to the question whether RRHs or eNBs are used as transmission points (TPs). Furthermore it depends on whether real physical eNBs are deployed (as shown in FIG. 3A) or virtual eNBs (e.g., offered by a pool of eNB computation resources) are used (as shown in FIG. 3B).
It is further to be noted that in the context of the present invention, an eNB may either be a real (i.e. physical eNB) or a virtual eNB (i.e. an instance of an eNB computational resource offered by a pool of computation power). A Transmission Point (TP) may be a Remote Radio Head (RRH) as well as a “complete” base station.
For further understanding of the present invention, FIGS. 4A to 4C depict examples of different known network topologies suitable for the implementation of the invention. The term Transmission Point (TP) may represent (an antenna or an antenna array of) either a RRH or a real physical eNB. FIG. 4A shows an example of a “bus” topological network structure, FIG. 4B a “star” topological network structure and FIG. 4C, a mixed “bus” and “star” topological network structure.